Abstract: Eight multiparous Holstein cows ((569±47) kg of BW;(84±17) DIM),were used in a replicated 4×4 Latin square design to evaluate the effects of different levels of ground wheat (GW) as replacements for ground corn (GC) in diets on metabolic parameters of nitrogen in dairy cows.The cows were allocated to the dietary treatments as follows (DM basis):W0 diet:total mixed ration (TMR) containing 0% GW and 27.9% GC;W9.6 diet: TMR containing 9.6% GW and 19.2% GC;W19.2 diet:TMR containing 19.2% GW and 9.6% GC;W28.8 diet:TMR containing 28.8% GW and 0% GC.The results indicated that milk production,percentage and yield of milk protein not affected by treatments;However,increasing dietary levels of GW,DM intake tended to increase quadratically (P=0.07),concentration of milk urea nitrogen (MUN) increased linearly (P<0.01),and significantly increased (P<0.01) in cows fed the W28.8 diet compared with the cows fed the W0 and W19.2 diets;Excretion of fecal nitrogen (N) not affected by diets,however,excretion of urinary N increased linearly (P<0.08);as a proportion of N intake,urinary N losses and total (urinary plus fecal) N losses tended to decrease quadratically (P=0.08);urinary urea N loss (P<0.01) and as a proportion of urinary N loss (P=0.03) increased linearly,and urinary urea N loss significantly increased (P=0.01) in cows fed the W19.2 and W28.8 diets,compared with other two diets;Urinary allantoin (P=0.05) and purines derivatives (P=0.09) tended to decrease linearly,microbial N synthesis significantly increased (P=0.02) in cows fed the W9.6 diet compared with the cows fed the W28.8 diet. Results from this experiment indicated that 9.6% of GW substitution for GC appeared to be an appropriate level in diet for early lactation dairy cows,a great amount of GW (28.8%) in the diets could increase the excretion of urinary N and urea N loss from the milk and urinary,and decrease microbial N supply.

Key words: Dairy cows, Wheat, Corn, Nitrogen metabolism, Microbial nitrogen

CLC Number: 

• S823